Sumitomo Electric Industries, Limited

Yoshiyuki Sugimoto

Keiji Tanaka

Seiji Kumagai

Makoto Ito

Taizo Tatsumi

Naoki Itabashi

Akihiro Moto

Sosaku Sawada

A reception circuit includes an input terminal configured to receive an input current; a voltage signal circuit being configured to convert a current signal into a voltage signal; a reference voltage circuit configured to generate a reference voltage in accordance with a first feedback current; a differential amplifier circuit configured to generate a differential signal in accordance with a voltage difference between the voltage signal and the reference voltage; and an offset control circuit configured to generate the first feedback current and a second feedback current, adjust the first feedback current when the voltage signal has an average voltage value greater than the reference voltage, and subtract the second feedback current from the input current such that the offset of the differential signal falls within the tolerance when the voltage signal has an average voltage value smaller than the reference voltage.

Reception circuit for optical communication

A receiver circuit includes an input terminal for receiving an input current signal, a transimpedance amplifier having an input node, the transimpedance amplifier converting a current signal input to the input node into a voltage signal, an inductor having a first terminal and a second terminal, and a bypass circuit. The first terminal is coupled to the input terminal and the second terminal is coupled to the input node. The bypass circuit includes a bias circuit supplying a bias voltage, a first variable resistor coupled between the first terminal and the bias circuit, a second variable resistor coupled between the second terminal and the bias circuit, and an impedance adjustment circuit including a resistor and a capacitor connected in parallel to the resistor, the impedance adjustment circuit connected in series to at least one of the first variable resistor and the second variable resistor.

Receiver circuit for optical communication

A receiving circuit includes a first input terminal and a second input terminal, an input circuit that includes a first node, a second node, a first inductor, a second inductor, a first variable resistive element, and a second variable resistive element. The first variable resistive element is electrically connected between the first node and the second input terminal, and the second variable resistive element is electrically connected between the second node and the first input terminal. The receiving circuit further includes a differential amplifier configured to generate a differential voltage signal in accordance with a differential current signal. The receiving circuit still further includes a control circuit configured to perform detection of an amplitude of the differential voltage signal and change a resistance value of the first variable resistive element and a resistance value of the second variable resistive element based on a result of the detection.

Receiving circuit and optical receiving circuit

A receiving circuit and an optical receiver including the receiving circuit are disclosed. The receiving circuit includes first and second input terminals, a FET, first and second TIA circuits, and a control circuit. The first and second input terminals each receive a current signal. The FET has first and second current terminals respectively connected to the first and second input terminals, and a control terminal. The first and second TIA circuits respectively are connected to the first and second current terminals, and convert the current signals to first and second voltage signals. The control circuit generates a control signal for application to the FET control terminal in accordance with a difference between the first and second voltage signals. The optical receiver includes the receiving circuit and each of first and second photodetectors for respectively supplying first and second current signals to the first and second input terminals of the receiver.

Receiving circuit and optical receiver

A variable resistance element is connected between a first input terminal of a first amplifier and a second input terminal of a second amplifier, and has a resistance value between the first input terminal and the second input terminal that is varied according to an amplitude value of a first voltage signal or an amplitude value or a differential voltage signal. A variable current source is connected between the first input terminal and a ground, and controls a current value of a current flowing to the ground from the first input terminal according to a value of an offset of the differential voltage signal. A bias voltage having the same value as that of a bias voltage that is applied to the first input terminal is applied to the second input terminal.

Transimpedance amplifier

A transimpedance amplifier circuit for generating an output voltage in accordance with an input current includes an offset resistor, a common emitter inverting amplifier having a first input and a first output, the first input receiving the input current, an emitter follower having a second input and a second output, the second input being coupled to the first output through the offset resistor, the second output outputting the output voltage, a feedback resistor connected between the second output and the first input, a variable current source connected to a node between the offset resistor and the second input, the variable current source configured to provide an offset current to the offset resistor, the offset current having a current value varied in accordance with a control signal, and a control circuit configured to generate the control signal so that an average voltage of the first output approaches a preset voltage value.

Transimpedance amplifier circuit

A differential amplifier circuit includes: a control current source supplying a control current; paired bipolar transistors; an a variable resistance circuit including: a series circuit of a first resistor and a second resistor having an identical resistance, the series circuit electrically connected between a first terminal and a second terminal of the variable resistance circuit; a first field effect transistor (FET) having a source and a drain being electrically connected to emitters of the paired bipolar transistors, respectively; and a second FET having a drain, a gate being electrically connected to the drain thereof, the gate of the first FET, and a control terminal of variable resistance circuit, a source being electrically connected to a connection node between the first resistor and the second resistor, wherein the control current source adjusts the control current to allow transconductance of the second FET to be kept constant.

Differential amplifier circuit having stable gain

A transimpedance amplifier includes a variable gain circuit configured to generate a pair of complementary signals in accordance with an input signal and a reference signal. A first differential circuit of the variable gain circuit includes a first transistor including a control terminal to receive the input signal, a second transistor including a control terminal to receive the reference signal, and a variable resistance circuit including a first field effect transistor (FET) and a second FET. A first timing when a voltage of a first linearity adjustment signal input to the first FET reaches a first threshold voltage of the first FET and a second timing when a voltage of a second linearity adjustment signal input to the second FET reaches a second threshold voltage of the second FET are different from each other.

Variable gain circuit and transimpedance amplifier using the same

An amplifier that amplifies a differential signal includes first and second input terminals for receiving two input signals; first and second diodes each including an anode and a cathode, the anodes being electrically connected to the first and second input terminals; first and second bias current sources being respectively electrically connected to the cathodes of the first and second diodes; an operational amplifier connected to the cathode of the first diode and the cathode of the second diode and configured to amplify a differential signal between signals generated at the cathodes of the first and second diodes; a capacitive element being electrically connected between an input and an output of the operational amplifier; and a differential amplifier provided between the operational amplifier and the first and second input terminals and configured to amplify the two input signals. The first and second bias current sources include a current mirror circuit.

Amplifier

A TIA converts a current signal received at its terminal to a voltage signal. The TIA includes an amplifier that includes an input node connected to the terminal and that converts a current signal received at the input node to a voltage signal; a first diode whose cathode is connected to the terminal; a second diode whose anode is connected to the terminal; a first current source connected to an anode of the first diode, the first current source supplying a first forward current to the first diode; a second current source connected to a cathode of the second diode, the second current source supplying a second forward current to the second diode; and a controller that controls forward currents respectively generated by the first current source and the second current source in accordance with an increase and decrease in the voltage signal.

Trans-impedance amplifier and optical receiver including the same

An amplifier includes a differential amplifier and a compensator. A differential amplifier includes a current source and paired transistors. The paired transistors generate an output signal by dividing a source current supplied by the current source into emitter currents of the paired transistors in response to a difference between an input signal and a reference signal. A compensator includes an amplifying transistor and a feedback circuit that feeds a collector current output from a collector of the amplifying transistor back to a base of the amplifying transistor therethrough. The compensator generates the reference signal at a base of the amplifying transistor. The compensator decreases power consumption of the amplifying transistor when the collector current increases, and increases the power consumption of the amplifying transistor when the collector current decreases. The compensator suppresses a peaking of gain in a low frequency band.

Amplifier with compensation of gain in low frequencies

A TIA comprises a TIA core that converts a current signal to a voltage signal, a single-to-differential converter that generates a differential voltage signal from the voltage signal, a feedback circuit that generates a control signal from the differential voltage signal, a bypass circuit that generates the current signal by subtracting the bypass current from the input current so that an average value of the current signal is maintained at a predetermined value, and a monitor circuit that generates a monitor current proportional to the bypass current from the control signal.

A TIA converts an input current into a output voltage. The TIA includes a feedback circuit that controls a bypass current to be extracted from the input current. The feedback circuit includes: a filter that passes low frequency components of the output voltage; a voltage shifter which includes a current source and converts an output signal of the filter into a first shift signal with a time constant; a voltage shifter which includes a current source, and converts a first threshold reference into a second shift signal with another time constant; a comparator which generates a control signal to control the bypass circuit by comparing the first shift signal with the second shift signal; and a comparator which controls the time constant by comparing the control signal with a second threshold reference.

An amplifier includes a first input terminal, a second input terminal, a TIA, and a compensation circuit. The TIA includes a first transistor, a second transistor, a first current source connected to the first input terminal and an emitter of the first transistor, a second current source connected to the second input terminal and an emitter of the second transistor, a first load resistor connected to a collector of the first transistor, and a second load resistor connected to a collector of the second transistor. A bias voltage is supplied to bases of the first and second transistors, the compensation circuit adjusts a first load current and a second load current based on voltage signals, and the TIA outputs the voltage signals based on collector voltages of the first and second transistors.

A differential circuit with a function to compensate unevenness observed in the differential gain thereof is disclosed. The differential circuit provides a low-pass filter in one of the paired transistors not receiving the input signal in addition to another low-pass filter that provides an average of output signals as a reference level of the differential circuit. The cut-off frequency of the filter is preferably set to be equal to the transition frequency at which the self-heating effect explicitly influences the trans-conductance of the transistor.

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Yokohama, Japan

Yoshiyuki Sugimoto